1. Field of the Invention
This invention relates sealed beam lamps, typically used with motor vehicles, and a method for inspection of the sealed beam lamps after assembly.
2. Description of the Prior Art
The prior art discloses a variety of sealed beam lamp designs. U.S. Pat. Nos. 3,904,904, 3,917,939, and 4,339,685 all illustrate sealed beam headlight assemblies wherein a burner capsule or illuminating bulb is enclosed within an outer envelope. The outer envelope is filled with an inert gas to maintain a contaminant free environment. Experience has shown this arrangement effectively minimizes degradation of the various internal components of the lamp such as the highly reflective coating of the reflector and the internal bulb supporting structure. Usually, the inert gas in the envelope is charged to a pressure slightly below atmospheric pressure. The lamp shown in U.S. Pat. No. 3,904,904 is fairly typical of the art insofar as it shows the inert gas at a pressure of about 620 Torrs (62 cm of mercury column at 20.degree. C.).
While sealed beam headlight arrangements such as the foregoing have proven to be satisfactory in most applications, heat generated in the burner capsule or illuminating bulb limits the service life of the sealed-beam lamp. Progressive deterioration of lamp components is caused by hot spots in the lens resulting from convection currents in the inert gas occurring during use of the lamp and contaminants leaking into the envelope. These problems are compounded by the difficulty of accurately verifying the integrity of the contaminent free environment within the envelope of the sealed beam lamp during manufacture.
There is, therefore, a need in the art to provide a sealed beam lamp which can be adequately cooled, is free of hot spots in the lens, and has a substantially reduced level of contaminants in the envelope.
In addition, there is also a need in the art to verify when such conditions have been achieved during lamp manufacture.